I had the same dilemma about which lens to pick a while back, the 24-70 or the 24-105. I ended up going with the 24-105. My experience has been that it is a good lens in terms of IQ; however, I've just had a hard time getting past the maximum aperture of 4.0. Most of what I shoot with is primes, so I'm used to the f/1.2 and f/1.4 range.
That being said, for some reason I haven't been able to sell it either. There are several things that it is great for, such as family portrait time at weddings when you want a higher aperture anyways to keep everyone in focus, or at the reception when you have a couple lights set up and typically go up to around f/4.0 anyways to get more of the action in focus. Another great use is for general purpose walk around lens, like when I just want to bring one lens while we take the kids to the zoo or something. Or in the studio.
So in any of those scenarios it's a better choice because it has more focal range than the 24-70. Plus it has Image Stabilization. (Although this may change soon if the rumors are true about a 24-70 f/2.8 IS II)
For wedding photography though, I would recommend the 24-70 f/2.8 over the 24-105 f/4.0. That extra stop will help in low light, plus it will give you better isolation of your subject from the background.
Now, if it were my money, I would ditch both options and go with the 16-35 f/2.8 if you like zooms, and if you favor primes, the 35 f/1.4 L.
The 16-35 would complement your 50 and 85 nicely, and it would also make a great focal range on your 50D while you had the 85 on your 5D MkII. The 35L also works like a champ and would give you a great line up of focal ranges of 35, 50, and 85, all of which are pretty fast lenses.